/*
 * Copyright (c) "Neo4j"
 * Neo4j Sweden AB [http://neo4j.com]
 *
 * This file is part of Neo4j.
 *
 * Neo4j is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
package org.neo4j.gds.ml.core.functions;

import org.neo4j.gds.ml.core.AbstractVariable;
import org.neo4j.gds.ml.core.ComputationContext;
import org.neo4j.gds.ml.core.Variable;
import org.neo4j.gds.ml.core.tensor.Tensor;

import java.util.List;

public abstract class SingleParentVariable<P extends Tensor<P>, T extends Tensor<T>> extends AbstractVariable<T> {
    protected final Variable<P> parent;

    public SingleParentVariable(
        Variable<P> parent,
        int[] dimensions
    ) {
        super(List.of(parent), dimensions);

        this.parent = parent;
    }

    @Override
    public Tensor<?> gradient(Variable<?> variable, ComputationContext ctx) {
        validateParent(variable);

        return gradientForParent(ctx);
    }

    protected abstract P gradientForParent(ComputationContext ctx);

    private void validateParent(Variable<?> variable) {
        if (variable != this.parent) {
            throw new RuntimeException("Calling gradient with a `parent` that was not expected");
        }
    }
}
